I. Field of the Invention
This invention relates to a machine for milling off old, cracked weld material from control rod drive penetrations used in nuclear boiling water reactor systems and more particularly to a machine that can rapidly be positioned and used so as to reduce the time exposure of workers to nuclear radiation.
II. Discussion of the Prior Art
The control rod drive (CRD) penetrations in a nuclear boiling water reactor (BWR) system have welded end caps. Intergranular stress corrosion cracking, (IGSCC), occurs at the weld interface because of the high heat, radiation, and fatigue environment of nuclear boiling water reactors. The cracked condition must be fixed before the function of the CRD is compromised.
To prevent compromise of the CRDs, one must enter the BWR's dry well, a high radiation area, to remove the old weld material and end caps from the CRD's whose welds exhibit IGSCC and then weld on new end caps. Protective suits are required in this high radiation area and an individual's exposure time in such a high radiation environment is limited by federal regulations. The removal of the old weld material has heretofore been a highly labor intensive procedure using a hack saw and an abrasive disk grinding wheel. Such a method is time consuming, inaccurate and results in air-borne contamination in the form of radioactive dust particles. Because of the limits on radiation exposure mandated by federal regulations, the time involved removing the old weld material necessarily limits the time for welding on the new end cap.
A need exists for a method which reduces time, eliminates inaccuracies and minimizes air borne contamination.
The primary object of this invention is to provide a device which shortens the time for removing old weld material from the CRDs in BWR installations.
Another object is to minimize the amount of air borne radioactive contamination in the form of radioactive dust.
Another object is to provide a manually adjustable device which readily clamps onto CRDs adjacent to the CRD to be milled for support.